[message] remove MessagePool from the Message::Metadata (#11616)

This commit simplifies the `Message::Metadata` so that it no longer
tracks the `MessagePool`. Instead the `Message` now tracks the
`ot::Instance` it is associated with and acts as a `GetProvider`,
allowing access to any component within `Instance`, including
the `MessagePool`.

src/core/common/locator.hpp

@@ -57,6 +57,15 @@ extern uint64_t gInstanceRaw[];
  * @{
  */
 
+#if !OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
+/**
+ * Gets the single OpenThread instance.
+ *
+ * @returns The single OpenThread instance.
+ */
+inline Instance &GetSingleInstance(void) { return *reinterpret_cast<Instance *>(&gInstanceRaw); }
+#endif
+
 /**
  * Implements `Get<Type>()` method for different `Type` objects belonging to the OpenThread
  * instance.
@@ -110,7 +119,7 @@ public:
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
     Instance &GetInstance(void) const { return *mInstance; }
 #else
-    Instance &GetInstance(void) const { return *reinterpret_cast<Instance *>(&gInstanceRaw); }
+    Instance &GetInstance(void) const { return GetSingleInstance(); }
 #endif
 
 protected:

src/core/common/message.cpp

@@ -66,7 +66,10 @@ Message *MessagePool::Allocate(Message::Type aType, uint16_t aReserveHeader, con
     VerifyOrExit((message = static_cast<Message *>(NewBuffer(aSettings.GetPriority()))) != nullptr);
 
     ClearAllBytes(*message);
-    message->SetMessagePool(this);
+
+#if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
+    message->GetMetadata().mInstance = &GetInstance();
+#endif
     message->SetType(aType);
     message->SetReserved(aReserveHeader);
     message->SetLinkSecurityEnabled(aSettings.IsLinkSecurityEnabled());
@@ -229,7 +232,7 @@ Error Message::ResizeMessage(uint16_t aLength)
     {
         if (curBuffer->GetNextBuffer() == nullptr)
         {
-            curBuffer->SetNextBuffer(GetMessagePool()->NewBuffer(GetPriority()));
+            curBuffer->SetNextBuffer(Get<MessagePool>().NewBuffer(GetPriority()));
             VerifyOrExit(curBuffer->GetNextBuffer() != nullptr, error = kErrorNoBufs);
         }
 
@@ -241,13 +244,13 @@ Error Message::ResizeMessage(uint16_t aLength)
     curBuffer  = curBuffer->GetNextBuffer();
     lastBuffer->SetNextBuffer(nullptr);
 
-    GetMessagePool()->FreeBuffers(curBuffer);
+    Get<MessagePool>().FreeBuffers(curBuffer);
 
 exit:
     return error;
 }
 
-void Message::Free(void) { GetMessagePool()->Free(this); }
+void Message::Free(void) { Get<MessagePool>().Free(this); }
 
 Message *Message::GetNext(void) const
 {
@@ -421,7 +424,7 @@ Error Message::PrependBytes(const void *aBuf, uint16_t aLength)
 
     while (aLength > GetReserved())
     {
-        VerifyOrExit((newBuffer = GetMessagePool()->NewBuffer(GetPriority())) != nullptr, error = kErrorNoBufs);
+        VerifyOrExit((newBuffer = Get<MessagePool>().NewBuffer(GetPriority())) != nullptr, error = kErrorNoBufs);
 
         newBuffer->SetNextBuffer(GetNextBuffer());
         SetNextBuffer(newBuffer);
@@ -769,7 +772,7 @@ Message *Message::Clone(uint16_t aLength) const
     uint16_t offset;
 
     aLength     = Min(GetLength(), aLength);
-    messageCopy = GetMessagePool()->Allocate(GetType(), GetReserved(), settings);
+    messageCopy = Get<MessagePool>().Allocate(GetType(), GetReserved(), settings);
     VerifyOrExit(messageCopy != nullptr, error = kErrorNoBufs);
     SuccessOrExit(error = messageCopy->AppendBytesFromMessage(*this, 0, aLength));
 

src/core/common/message.hpp

@@ -190,6 +190,9 @@ public:
 protected:
     struct Metadata
     {
+#if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
+        Instance *mInstance;
+#endif
         bool mDirectTx : 1;            // Whether a direct transmission is required.
         bool mLinkSecurity : 1;        // Whether link security is enabled.
         bool mInPriorityQ : 1;         // Whether the message is queued in normal or priority queue.
@@ -227,13 +230,12 @@ protected:
 #if OPENTHREAD_CONFIG_TIME_SYNC_ENABLE
         int64_t mNetworkTimeOffset; // The time offset to the Thread network time, in microseconds.
 #endif
-        TimeMilli    mTimestamp;   // The message timestamp.
-        Message     *mNext;        // Next message in a doubly linked list.
-        Message     *mPrev;        // Previous message in a doubly linked list.
-        MessagePool *mMessagePool; // Message pool for this message.
-        void        *mQueue;       // The queue where message is queued (if any). Queue type from `mInPriorityQ`.
-        RssAverager  mRssAverager; // The averager maintaining the received signal strength (RSS) average.
-        LqiAverager  mLqiAverager; // The averager maintaining the Link quality indicator (LQI) average.
+        TimeMilli   mTimestamp;   // The message timestamp.
+        Message    *mNext;        // Next message in a doubly linked list.
+        Message    *mPrev;        // Previous message in a doubly linked list.
+        void       *mQueue;       // The queue where message is queued (if any). Queue type from `mInPriorityQ`.
+        RssAverager mRssAverager; // The averager maintaining the received signal strength (RSS) average.
+        LqiAverager mLqiAverager; // The averager maintaining the Link quality indicator (LQI) average.
 #if OPENTHREAD_FTD
         ChildMask mChildMask; // ChildMask to indicate which sleepy children need to receive this.
 #endif
@@ -479,7 +481,11 @@ public:
      *
      * @returns A reference to the `Instance`.
      */
-    Instance &GetInstance(void) const;
+#if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
+    Instance &GetInstance(void) const { return *GetMetadata().mInstance; }
+#else
+    Instance &GetInstance(void) const { return GetSingleInstance(); }
+#endif
 
     /**
      * Frees this message buffer.
@@ -1546,9 +1552,6 @@ private:
         AsConst(this)->GetNextChunk(aLength, static_cast<Chunk &>(aChunk));
     }
 
-    MessagePool *GetMessagePool(void) const { return GetMetadata().mMessagePool; }
-    void         SetMessagePool(MessagePool *aMessagePool) { GetMetadata().mMessagePool = aMessagePool; }
-
     bool IsInAQueue(void) const { return (GetMetadata().mQueue != nullptr); }
     void SetMessageQueue(MessageQueue *aMessageQueue);
     void SetPriorityQueue(PriorityQueue *aPriorityQueue);
@@ -1916,8 +1919,6 @@ private:
     uint16_t mMaxAllocated;
 };
 
-inline Instance &Message::GetInstance(void) const { return GetMessagePool()->GetInstance(); }
-
 /**
  * @}
  */